1. Field of the Invention
The present invention relates to a liquid crystal display device, more particularly to the method of arranging a flexible printed circuit board connected to a liquid crystal display panel.
2. Description of the Prior Art
A conventional type of a liquid crystal display device of the active matrix type is mainly made up of a liquid crystal display panel where switching devices corresponding to pixel electrodes are arrayed in a matrix state, and a flexible printed circuit board is connected to the switching devices to supply display data, power and the like, and a backlight unit illuminates the liquid crystal display panel.
Such a liquid crystal display device is widely used as the display device for various kinds of equipment such as car navigation devices, laptop personal computers and small-sized television sets, where the size of the liquid crystal display panel varies depending on its application, and the length of the flexible printed circuit board connected to the panel is also variable.
The flexible printed circuit board usually comprises a board of such flexibility where one end thereof connected to the liquid crystal display panel is broader than the other end of the board connected to an interface circuit board.
FIG. 9 is a plane view showing an example of a publicly-known flexible printed circuit board. The flexible printed circuit board 30 is approximately T-shaped where its width tapers from one end 30a toward the other end 30b with the end 30a and the end 30b being connected to the liquid crystal display panel and the interface circuit board, respectively. Specifically, in the flexible printed circuit board, assuming that the width of the T-shaped head portion 30a is “a” and the width of the leg portion 30b is “b”, the relationship between a and b is [a>b]. Width a is determined by the size and the number of pixels or the like of the liquid crystal display panel, while width b is determined by the size of the connector mounted on the interface circuit board.
Meanwhile, the high definition and color display qualities of liquid crystal display panels have progressed in recent years, and the number of pixels and electrodes has become larger. Since the number of wirings connected to the electrodes has increased, the width a of the end portion 30a of the flexible printed circuit board connected to the wirings has also become wider.
On the other hand, because the size of the connector mounted on the interface circuit board has become smaller, the width b of the end portion 30b of the flexible printed circuit board has become narrower.
For this reason a large number of wirings, specifically wirings 31a to 31n, are arranged from the T-shaped head portion of the flexible printed circuit board as to converge toward the leg portion thereof. In other words, the large numbers of wirings 31a to 31n are wired such that their width and pitch gradually become narrower as they approach the leg portion.
However, since the wirings wired to the flexible printed circuit board are numerous, a longer wiring path is required to make the width and the pitch of the wirings conform to the tapering T-shaped leg portion 30b. 
Since the wiring path usually causes the wirings to converge at the T-shaped head portion which is wider than the T-shaped leg portion, the width “c” of the T-shaped head portion becomes longer in proportion to the thickness of wirings, the number of wirings and the width of leg portion. However, when the T-shaped head portion is lengthened, the flexible printed circuit board itself becomes longer as to require housing-thereof in the device. Various methods have been introduced to solve this problem, one of which is disclosed in Japanese Laid-Open Patent Publication Nos. 9-138388 (FIG. 26, Paragraphs [0071] and [0072]), 10-39779 (FIG. 6, Paragraphs [0021] to [0024]) and 11-38431 (FIG. 3, Paragraphs [0034] and [0035]).
The above-mentioned Japanese Laid-Open Patent Publication Nos. 9-138388 and 10-39779 refer to a liquid crystal display device where the flexible printed circuit board is folded on the rear surface of the liquid crystal display panel and housed between the liquid crystal display panel and the backlight.
Further, FIG. 10 is a cross-sectional view showing a liquid crystal display device described in the above-mentioned Japanese Laid-Open Patent Publication No. 11-38431, where the flexible printed circuit board is folded a number of times like an accordion and housed in the liquid crystal display device.
A liquid crystal display device 20 has a liquid crystal display panel PNL in which a liquid crystal layer is formed between two transparent glass substrates SUB1, SUB2, a light guiding plate 21 that illuminates the display panel, and parts such as a fluorescent tube 22 that leads out light to the light guiding plate, and these parts are housed in a lower shield case LF and fixed by an upper shield case SHD. A flexible printed circuit board FPC is connected to drive IC chips installed on the glass substrate SUB1, folded threefold approximately perpendicular to the display surface of the liquid crystal display panel PNL, and housed in the lower shield case LF.
The flexible printed circuit board of the liquid crystal display device disclosed in Japanese Laid-Open Patent Publication Nos. 9-138388 and 10-39779 is inserted between the liquid crystal display panel and the light guiding plate, while the flexible printed circuit board of liquid crystal display device disclosed in Japanese Laid-Open Patent Publication No. 11-38431 is housed by being folded in the vertical direction therein. Although the flexible printed circuit board can be housed in the device in accordance with these methods when it is relatively short, housing becomes extremely difficult when the board is made longer due to limited housing space in the device.